The novel went through “many, many drafts,” she says. “It was in fact told in the voice of the fire for the first draft—for the first several versions of that draft. And the next draft is all told in the voice of William,” a somewhat mysterious character whose path intersects with Katherine’s several times during the book and who helps supply the novel’s guardedly hopeful ending. “I could tell you everything about William, but you know very little” about him in the book as published, Kephart says.

“For every sentence you see there, not only has that sentence gone through multiple changes, but I take out 70 percent. Even when I think I’m done, after all of the layers, I take out about 70 percent,” she adds. “Just as I did with memoir, I work toward certain themes. And I don’t want anything to get in the way of those themes.”

(Kephart’s fascination with the city’s history clashed with her book’s rigorous structural requirements—there was a lot she wasn’t able to squeeze in. She resolved the conflict by creating her own teacher’s guide for the book, which provides information on how the Centennial was organized and funded, the exhibition buildings—of which only Memorial Hall, now the Please Touch Museum, remains—and highlighting figures who receive only fleeting mention in the book, like Elizabeth Duane Gillespie, “Benjamin Franklin’s great-granddaughter, a tremendous feminist who made the Women’s Pavilion on the Centennial grounds possible,” and George Childs, philanthropist and editor of the Philadelphia Public Ledger newspaper, whom Kephart calls “my hero” and “my favorite Philadelphian.”)

Kephart was first attracted to the memoir form when she stumbled on Natalie Kusz’s Road Song, about her experiences after her family moved from Los Angeles to Alaska when she was six years old, in a Princeton bookshop years ago. “I was stunned by that form, by the quietude that Kusz brought to her personal story.”

Though she remains “very comfortable with that ‘I’ voice,” after having written several memoirs she felt that she had come to a kind of end. “Really I thought, when I wrote Ghosts in the Garden, which was my fifth book, that it would be my last. And then the river beckoned.”

Kephart calls Flow “perhaps the most true of my books. I understand that river very well. I understand her heartbreak, her losses,” she says. “And then I discovered, ‘Wow, I can move toward fiction.’”

Laura Geringer—then an editor with HarperCollins’ HarperTeen division and now with Egmont USA, which published Dangerous Neighbors—had written Kephart a long letter in which, “she basically said, “I’d love to see you writing young adult fiction,’” Kephart recalls.

In 2001, Kephart had chaired the National Book Awards Young People’s Literature jury, “which forced me to read about 165 books,” she says. She also had a long history of teaching writing to children, which is a theme in the memoir, Seeing Past Z, “so I kind of knew what [young people] were interested in and what they were reading and what they were aspiring toward.” Nevertheless, she was unfamiliar with the most popular young-adult novel series—and still hasn’t read them, she says—and was reluctant to write in the genre “because I didn’t know how it was done.”

It took about a year of back and forth, but she changed her mind after Geringer paid a visit to Philadelphia to meet with her. “She asked me what I had been like as a teenager in high school during our conversation down here,” Kephart recalls. “And I told her, you know, ‘I was an ice skater. I was rather invisible. I wrote poems. Boring.’ And I kept deflecting, as I always do. And she said, when we were walking back to the train station, ‘[That] sounds interesting to me.’”

“And I got on the train, had some scrap paper, wrote the first 10 pages of Undercover. And that’s how that book started,” she says. “And it became very meaningful to me. I [have] really enjoyed writing those books. And all of those characters have so many pieces of me in them.”

Another satisfaction was the interactions she began having with her audience. “I got involved in this whole blogosphere, and I started to hear from these young readers,” Kephart says. “And the sort of ecstatic high of interacting with young people in that way was tremendous. And sometimes I get to meet them now.”

While the designation YA is “meaningful to the publishing house and to the bookstores that have to shelve those books,” she says, it has limited value for readers. “I would suggest that 65, 75 percent of my readership is adult.”

Of her novels so far, she considers Undercover and The Heart is Not a Size, which deals with anorexia in a story of two friends who go on a school-service trip to Mexico, as being closest to a conventional young adult novel “because of the conflict at that youth level.” But a book like Nothing but Ghosts, about a young woman whose mother has died “was very meaningful to a lot of women my age who have just lost their mother,” Kephart says. “A lot of my books have these adult interactions.” In the case of Dangerous Neighbors, Katherine and Anna are 19 years old, she notes. “The writing is clearly for anybody who wants to read a book decorated with lyrical prose. So I never ever write to genre or category. Good or bad, I don’t know.”